1. Field of the Invention
The present invention is related to an electronic circuit device and in particular, is related to an electronic circuit device which includes a magnetic body within a resin sealing body and which his used as a power supply module included in a power supply unit.
2. Description of the Related Art
For example, a DC-DC converter is incorporated in a power supply unit of a general purpose television. The DC-DC converter, for example, coverts a direct current voltage converted from a general household 100 V alternating current, into an alternating current used in a control circuit unit or drive circuit unit. The DC-DC converter finally produces a 12 V or 24 V direct current voltage.
Thinner and smaller scale power supply units are an important issue in the development of general purpose televisions such as LCD and plasma televisions which tend to have thin, flat and large screens. If a electronic circuit device in which a plurality of electronic parts which form a DC-DC converter are packaged is manufactured as one power supply module, it becomes easier to realize thinner and smaller scale power supply units and more easily manageable when incorporating these power supply units within electronic circuit devices.
In a DC-DC converter, a transformer is used in direct current voltage conversion. The transformer is arranged with a core comprised of a magnetic body material and a coil wound around the core. For example, in the case where a transformer is made into a resin mold using a transfer mold technique, there is concern that the stress produced from the difference between the linear expansion coefficient of the core of a transformer and the linear expansion coefficient of the resin, will extend to the core.
A stress relieving transformer which relieve stress and impact cause by resin after the resin is molded and which is strong to the degradation of magnetic properties or breaks in the core is disclosed in Japanese Laid Open Patent 2002-164229 (Patent Document 1).
This stress relieving transformer includes a ferritic core and a coil bobbin and the entire surface of the ferritic core and a gap between the ferritic core and coil bobbin is covered by a buffer resin and also includes a structure which covers the exterior of this buffer resin with an outer layer resin which has a high Young modulus.
In addition, a ferritic core is disclosed in Japanese Laid Open Patent 1991-012906 (Patent Document 2) in which the surface of a ferritic core is covered by an interior layer which is comprised from a resin which has excellent elastic properties and this interior layer is further coated with an exterior resin layer which has excellent electrical insulation properties.
However, the following points were not considered in the stress relieving transformer disclosed in Patent Document 1 and the ferritic core disclosed in Patent Document 2 stated above.
The stress relieving transformer disclosed in Patent Document 1 has a ferritic core and coil bobbin which are covered by two layers comprising the buffer resin and exterior resin layer and moreover has a structure which covers the entire ferritic core. However, the main body of the ferritic core disclosed in the Patent Document 2 is covered by two layers comprising an interior layer and an exterior resin layer and the ferritic core has a structure which covers the entire body. Both have a two layered resin structure and while the structures become complex, overall they are thin and it is difficult to simultaneously realize relief of the stress produced on the ferritic core and thin and small scale electronic circuit devices which uses this ferritic core.